Electromyography of brachial muscles in Pan troglodytes and Pongo pygmaeus

Electromyographic recordings were taken from all heads of the triceps brachii and biceps brachii muscles and from the anconeus, brachialis, and brachioradialis muscles in a chimpanzee and an orangutan as they stood still and walked quadrupedally on horizontal and inclined surfaces, engaged in suspensory behavior, reached overhead, and manipulated a variety of foods and artifacts. Like the gorilla (Tuttle and Basmajian, 1974a), the chimpanzee and orangutan possess special close-packed positioning mechanisms that allow the bulky muscles that cross their elbow joints to remain silent during quiet pendant suspension. We found no major myological features that would dramatically separate the arms of knuckle-walking African apes from those of the orangutan. With a few exceptions, which could as well be attributed to individual variation as to interspecific differences, the brachial muscles acted similarly during quadrupedal positional behaviors, irrespective of whether the hands of the subjects were knuckled (African apes), fisted (chimpanzee and orangutan), or placed in modified palmigrade postures (orangutan). Evolutionary transformations, from brachial and elbow complexes like those of Pongo to ones like Pan, or vice versa, would probably be achieved quite readily as the species changed its substrate preferences and positional habits.     

Brief communication: Swimming and diving behavior in apes (Pan troglodytes and Pongo pygmaeus): First documented report

Extant hominoids, including humans, are well known for their inability to swim instinctively. We report swimming and diving in two captive apes using visual observation and video recording. One common chimpanzee and one orangutan swam repeatedly at the water surface over a distance of 2–6 m; both individuals submerged repeatedly. We show that apes are able to overcome their negative buoyancy by deliberate swimming, using movements which deviate from the doggy‐paddle pattern observed in other primates. We suggest that apes' poor swimming ability is due to behavioral, anatomical, and neuromotor changes related to an adaptation to arboreal life in their early phylogeny. This strong adaptive focus on arboreal life led to decreased opportunities to interact with water bodies and consequently to a reduction of selective pressure to maintain innate swimming behavior. As the doggy paddle is associated with quadrupedal walking, a deviation from terrestrial locomotion might have interfered with the fixed rhythmic action patterns responsible for innate swimming. Am J Phys Anthropol 152:156–162, 2013. © 2013 Wiley Periodicals, Inc.     

Comparing the performances of apes (Gorilla gorilla, Pan troglodytes, Pongo pygmaeus) and human children (Homo sapiens) in the floating peanut task

Recently, Mendes et al. [1] described the use of a liquid tool (water) in captive orangutans. Here, we tested chimpanzees and gorillas for the first time with the same "floating peanut task." None of the subjects solved the task. In order to better understand the cognitive demands of the task, we further tested other populations of chimpanzees and orangutans with the variation of the peanut initially floating or not. Twenty percent of the chimpanzees but none of the orangutans were successful. Additional controls revealed that successful subjects added water only if it was necessary to obtain the nut. Another experiment was conducted to investigate the reason for the differences in performance between the unsuccessful (Experiment 1) and the successful (Experiment 2) chimpanzee populations. We found suggestive evidence for the view that functional fixedness might have impaired the chimpanzees' strategies in the first experiment. Finally, we tested how human children of different age classes perform in an analogous experimental setting. Within the oldest group (8 years), 58 percent of the children solved the problem, whereas in the youngest group (4 years), only 8 percent were able to find the solution.     

Functional ecology and evolution of hominoid molar enamel thickness: Pan troglodytes schweinfurthii and Pongo pygmaeus wurmbii

The divergent molar characteristics of Pan troglodytes and Pongo pygmaeus provide an instructive paradigm for examining the adaptive form-function relationship between molar enamel thickness and food hardness. Although both species exhibit a categorical preference for ripe fruit over other food objects, the thick enamel and crenulated occlusal surface of Pongo molar teeth predict a diet that is more resistant to deformation (hard) and fracture (tough) than the diet of Pan. We confirm these predictions with behavioral observations of Pan troglodytes schweinfurthii and Pongo pygmaeus wurmbii in the wild and describe the mechanical properties of foods utilized during periods when preferred foods are scarce. Such fallback foods may have exerted a selective pressure on tooth evolution, particularly molar enamel thinness, which is interpreted as a functional adaptation to seasonal folivory and a derived character trait within the hominoid clade. The thick enamel and crenulated occlusal surface of Pongo molars is interpreted as a functional adaptation to the routine consumption of relatively tough and hard foods. We discuss the implications of these interpretations for inferring the diet of hominin species, which possessed varying degrees of thick molar enamel. These data, which are among the first reported for hominoid primates, fill an important empirical void for evaluating the mechanical plausibility of putative hominin food objects.     

Foramen magnum position variation in Pan troglodytes, Plio-Pleistocene hominids, and recent Homo sapiens: implications for recognizing the earliest hominids

The anteroposterior position of the foramen magnum distinguishes living Homo sapiens from apes, and has been used as evidence for the hominid status of numerable fossils in the history of human paleontology. During the past decade, foramen magnum position has been cited as evidence of the hominid status of Ardipithecus and Sahelanthropus. Specifically, the basion of Ardpithecus is reported to be inline with the bicarotid chord, while the basion of Sahelanthropus is reported to both touch the biporion chord and intersect the bicarotid chord. In order to assess the effectiveness of anteroposterior foramen magnum position in distinguishing hominids from nonhominid apes, this study examined whether or not the positions of biporion and bicarotid relative to basion sufficiently distinguished Pan troglodytes from recent Homo sapiens and Plio-Pleistocene hominids. The distances from basion to the biporion chord (BSBIP) and from basion to the bicarotid chord (BSBIC) were measured on samples of chimpanzee (n = 69) and recent human (n = 42) crania and a sample of Plio-Pleistocene hominid fossils (n = 8). The data were used to test the hypothesis that BSBIP and BSBIC measurements do not sufficiently distinguish P. troglodytes from hominids. While basion to biporion (BSBIP) does not effectively distinguish P. troglodytes from Plio-Pleistocene hominids and humans when used univariately, basion to bicarotid (BSBIC), when used univariately or bivariately with BSBIP, can be used to test whether or not an unknown specimen is a hominid. These results are used to evaluate the hominid status of Ardipithecus and Sahelanthropus.     

Locomotor ecology of wild orangutans (Pongo pygmaeus abelii) in the Gunung Leuser Ecosystem, Sumatra, Indonesia: a multivariate analysis using log-linear modelling

The large body mass and exclusively arboreal lifestyle of Sumatran orangutans identify them as a key species in understanding the dynamic between primates and their environment. Increased knowledge of primate locomotor ecology, coupled with recent developments in the standardization of positional mode classifications (Hunt et al. [1996] Primates 37:363-387), opened the way for sophisticated multivariate statistical approaches, clarifying complex associations between multiple influences on locomotion. In this study we present a log-linear modelling approach used to identify key associations between orangutan locomotion, canopy level, support use, and contextual behavior. Log-linear modelling is particularly appropriate because it is designed for categorical data, provides a systematic method for testing alternative hypotheses regarding interactions between variables, and allows interactions to be ranked numerically in terms of relative importance. Support diameter and type were found to have the strongest associations with locomotor repertoire, suggesting that orangutans have evolved distinct locomotor modes to solve a variety of complex habitat problems. However, height in the canopy and contextual behavior do not directly influence locomotion: instead, their effect is modified by support type and support diameter, respectively. Contrary to classic predictions, age-sex category has only limited influence on orangutan support use and locomotion, perhaps reflecting the presence of arboreal pathways which individuals of all age-sex categories follow. Effects are primarily related to a tendency for adult, parous females to adopt a more cautious approach to locomotion than adult males and immature subjects.     

Interspecific and Ontogenetic Variation in Proximal Pedal Phalangeal Curvature of Great Apes (Gorilla gorilla, Pan troglodytes, and Pongo pygmaeus)

Considerable attention has been devoted to understanding phalangeal curvature in primates, particularly with regard to locomotion. Previous work has found that increased phalangeal curvature may be indicative of increased grasping during suspensory and climbing behaviors, but the details of this relationship, particularly as regards feet, is still unclear. Using behavioral studies to predict an interspecific gradient of variation in pedal phalangeal curvature, I collected digital data from the third and fifth digit proximal pedal phalanges in adult Gorilla gorilla, Pan troglodytes, and Pongo pygmaeus and calculated included angles of phalangeal curvature to assess the appropriateness of pooling digits within taxa and evaluate the association between variation in pedal phalangeal curvature and frequency of climbing behavior. I also used an ontogenetic sample of Pan troglodytes to evaluate the postnatal relationship between variation in phalangeal curvature and grasping behaviors. I found intraspecific variation in phalangeal curvature suggesting among-digit variation in grasping behaviors. Curvature of Pongo was significantly greater than of both Pan and Gorilla. In contrast, Pan was significantly more curved than Gorilla only in comparison of third digits. Ontogenetic decreases in pedal phalangeal curvature among Pan troglodytes accorded well with postnatal decreases in documented climbing frequency. These findings largely support earlier work regarding the association between arboreal grasping and phalangeal curvature, and provide a unique intraspecific analysis that illuminates a number of areas where our knowledge of the behavioral and biomechanical determinants of phalangeal curvature should be explored further, particularly with respect to the role of among-digit variation in phalangeal curvature.     

Comparative analysis of sperm motility in liquid and seminal coagulum portions between Bornean orangutan (Pongo pygmaeus) and chimpanzee (Pan troglodytes)

Coagulum in the semen of some primates plays different roles, depending on the species. In the present study, we examined sperm motility in the coagulum and liquid portions of semen collected from captive individuals from two great ape species: two adult Bornean orangutans (Pongo pygmaeus) (n?=?27) and three adult chimpanzees (Pan troglodytes) (n?=?14). The results revealed that orangutan sperm remained motile for significantly longer in the coagulum than in the liquid portion (>?18 h). By contrast, chimpanzee sperm motility did not differ significantly over time between the two portions of the semen, although motility was slightly higher in the liquid portion than in the coagulum. The evolution of the seminal coagulum is thought to be related to postcopulatory sperm competition; however, functions of seminal coagulum have not been completely elucidated. Our data from the orangutan semen suggest that in this species, seminal coagulum may strengthen own-sperm survival. This report is the first to provide evidence for this distinctive function of the seminal coagulum. This unique property of orangutan seminal coagulum might be attributable to their reproductive traits, e.g., difficulty in predicting ovulation due to a lack of genital swelling during estrus. The orangutan is a Critically Endangered species, and captive breeding, including artificial insemination (AI), is expected. However, worldwide, only one case of orangutan AI has been successful. Our findings may contribute to an understanding of their basic semen characteristics and help improve the AI method.

     

Correction to: Comparative analysis of sperm motility in liquid and seminal coagulum portions between Bornean orangutan (Pongo pygmaeus) and chimpanzee (Pan troglodytes)

Primates - In the original publication of the article, the coauthor “Takashi Hayakawa” was wrongly assigned as co-corresponding author.     

Dissociation of cortisol and behavioral indicators of stress in an orangutan (Pongo pygmaeus) during a computerized task

Computerized testing can induce behavioral signs of frustration in apes. Three variations of a computer task were used to investigate the effects of inter-trial intervals and rate of cursor movement on frustrative behavior and cortisol in an orangutan. Behaviors were recorded during test sessions, and saliva was collected immediately after test sessions for cortisol assay. Behavioral results indicated that extended (20 sec) periods of delay between trials induced signs of frustration in the subject, including forceful manual manipulation of objects and self-scratching. However, cortisol results indicated that Hypothalamic-Pituitary-Adrenal (HPA) axis activity was not induced by task performance. Rather, cortisol levels were reduced during performance of computer tasks compared to baseline levels. Findings from this study suggest that behavioral and cortisol responses to stress induced by performance of computer testing can become dissociated. This study validates salivary cortisol as a measure of HPA activity in apes and demonstrates a normal circadian rhythm of cortisol release in an orangutan.     

The effects of linear perspective on relative size discrimination in chimpanzees (Pan troglodytes) and humans (Homo sapiens)

In this study, we tested the corridor illusion in three chimpanzees and five humans, applying a relative size discrimination task to assess pictorial depth perception using linear perspective. The subjects were required to choose the physically larger cylinder of two on a background containing drawn linear perspective cues. We manipulated both background and cylinder size in each trial. Our findings suggest that chimpanzees, like humans, exhibit the corridor illusion.     

Morphological evolution through integration: a quantitative study of cranial integration in Homo, Pan, Gorilla and Pongo

Morphological integration refers to coordinated variation among traits that are closely related in development and/or function. Patterns of integration can offer important insight into the structural relationship between phenotypic units, providing a framework to address questions about phenotypic evolvability and constraints. Integrative features of the primate cranium have recently become a popular subject of study. However, an important question that still remains under-investigated is: what is the pattern of cranial shape integration among closely related hominoids? To address this question, we conducted a Procrustes-based geometric morphometrics study to quantify and analyze shape covariation patterns between different cranial regions in Homo, Pan, Gorilla and Pongo. A total of fifty-six 3D landmarks were collected on 407 adult individuals. We then sub-divided the landmarks corresponding to cranial units as outlined in the ‘functional matrix hypothesis.’ Sub-dividing the cranium in this manner allowed us to explore patterns of covariation between the face, basicranium and cranial vault, using the two-block partial least squares approach. Our results suggest that integrated shape changes in the hominoid cranium are complex, but that the overall pattern of integration is similar among human and non-human apes. Thus, despite having very distinct morphologies the way in which the face, basicranium and cranial vault covary is shared among these taxa. These results imply that the pattern of cranial integration among hominoids is conserved.     

The Risk of Disease to Great Apes: Simulating Disease Spread in Orang-Utan (Pongo pygmaeus wurmbii) and Chimpanzee (Pan troglodytes schweinfurthii) Association Networks

All great ape species are endangered, and infectious diseases are thought to pose a particular threat to their survival. As great ape species vary substantially in social organisation and gregariousness, there are likely to be differences in susceptibility to disease types and spread. Understanding the relation between social variables and disease is therefore crucial for implementing effective conservation measures. Here, we simulate the transmission of a range of diseases in a population of orang-utans in Sabangau Forest (Central Kalimantan) and a community of chimpanzees in Budongo Forest (Uganda), by systematically varying transmission likelihood and probability of subsequent recovery. Both species have fission-fusion social systems, but differ considerably in their level of gregariousness. We used long-term behavioural data to create networks of association patterns on which the spread of different diseases was simulated. We found that chimpanzees were generally far more susceptible to the spread of diseases than orang-utans. When simulating different diseases that varied widely in their probability of transmission and recovery, it was found that the chimpanzee community was widely and strongly affected, while in orang-utans even highly infectious diseases had limited spread. Furthermore, when comparing the observed association network with a mean-field network (equal contact probability between group members), we found no major difference in simulated disease spread, suggesting that patterns of social bonding in orang-utans are not an important determinant of susceptibility to disease. In chimpanzees, the predicted size of the epidemic was smaller on the actual association network than on the mean-field network, indicating that patterns of social bonding have important effects on susceptibility to disease. We conclude that social networks are a potentially powerful tool to model the risk of disease transmission in great apes, and that chimpanzees are particularly threatened by infectious disease outbreaks as a result of their social structure.